The demand for optical fiber cable is increasing according to the implementation of diversified communication services, such as bidirectional communication and video call, and increase of LAN service.
Due to their high communication performance, the demand for optical fiber cable is increasing sharply to meet the increase of such communication services.
The typical optical fiber cable comprises one or more optical fiber units having one or more optical fiber cores and buffer tube or tubes covering the cores, and the optical fiber units are covered with outer sheath.
Since optical fiber cables are usually installed in wet environment, for example, underground pit or the sea-bed, they must be protected from the moisture or water to maintain the communication functionality.
The typical waterproof methods for optical fiber cable can be classified into three categories.
The three methods are inserting jelly compound in the optical fiber cable, inserting waterproof powder in the tube, and applying water-blocking tape containing waterproofing material.
The first method, inserting jelly compound in the cable, has the inconvenience of removing the jelly using special detergent or alcohol when the cable is cut off for branch joint, and contamination of environment may be occurred by the jelly material.
The method of applying water-blocking tape is difficult to be implemented, because the process of inserting water-blocking tape into the tube is not simple.
And, the method using waterproof powder has a matter that waterproof power is liable to be weakened over a long period, because the waterproof powder in the cable may move in the cable.
To solve these problems, the method of applying waterproof yarn containing waterproof material in cable is suggested.
In this method, a certain quantity of the waterproof yarn is applied in optical fiber cable to absorb the moisture penetrated into the tube.
In the waterproof yarn, waterproof powder is applied which absorbs the moisture in cable.
The waterproof yarn can be wound on the buffer tube or sheath, or laid longitudinally into the buffer tube.
The waterproof yarn may be broken by tensile stress in the process of application in the buffer tube or by cable bending, for example, during cable laying or winding on a cable drum, and that can lead to deterioration of waterproof performance.
In addition, the thermal expansion or shrinkage of the waterproof yarn may cause interference of the waterproof yarn with the optical fiber unit and that can cause optical loss.